VIENNA -- Iran and six world powers
ended the opening round of nuclear talks
on an upbeat note Thursday, with both sides saying they had agreed on a plan
for further negotiations meant to produce a comprehensive deal to set limits on
Tehran's nuclear ambitions.

In a joint statement, they said the
next round of negotiations would begin in Vienna on March 17, continuing a
process likely to take at least six months and probably longer.

Expectations had been modest as the talks started Tuesday, and the upbeat tone on
a framework for future talks appeared
aimed in part to encourage skeptics inside and outside Iran that the
negotiations had a chance to succeed despite huge gaps between the Iranians and
the six powers.

The six want Tehran to agree to
significant cuts in its nuclear program to reduce concerns it could be turned
quickly to weapons use.

Iran opposes cuts, saying its program
is not aimed at building weapons. The U.S. and its partners say that Iran must
come to an agreement if it wants a full end to sanctions crippling its economy.

"We have ... identified all of
the issues we need to address for a comprehensive and final agreement,"
said Catherine Ashton, the EU's top diplomat who convened the talks between Iran and the six powers - the
United States, Russia, China, Britain, France and Germany.

"It won't be easy, but we've
gotten off to a good start," she said in a statement read later in Farsi
by Iranian Foreign Minister Mohammad Javad Zarif.

A Western diplomat said Ashton would
visit Tehran March 9-10 for preparatory talks.
He demanded anonymity because his information was confidential.

"The talks
are designed to build on a first-step deal in effect since last month that
commits Iran to initial nuclear curbs in return for some easing of sanctions.
The deal can be extended by mutual consent after six months. Both sides say any
final deal will be tough to reach.

The six countries want to leave Iran
with little capacity to quickly ramp up its nuclear program into weapons-making
mode with enriched uranium or plutonium, which can be used for the fissile core
of a missile warhead.

They say Iran should dismantle or
store most of its 20,000 uranium-enriching centrifuges, including some not yet
working. They also want a reactor now being built to either be scrapped or
converted from a heavy-water setup to a light-water facility that makes less
plutonium.

Zarif, who came to the talks vowing Iran would never strip down its
nuclear facilities, was smiling and relaxed as he read out the joint statement.
But in a message intended for skeptics at home who fear Iran will give up too
much at the talks, he told state TV
afterward that the nation would "not close down any site."